This invention relates to articles which require wear-resistance, such as components used in turbine engines. In some specific embodiments, it relates to improved techniques for applying such coatings to surfaces that are difficult to access.
Components are used in a wide variety of industrial applications, under a diverse set of operating conditions. In many cases, the components are provided with coatings which impart various characteristics, such as corrosion resistance, heat resistance, oxidation resistance, and wear resistance. As an example, the various components of turbine engines are often coated with thermal barrier coatings, to effectively increase the temperature at which they can operate.
The wear-resistant coatings (often referred to as xe2x80x9cwear coatingsxe2x80x9d) are frequently used on turbine engine components, such as nozzle wear pads and dovetail interlocks. The coatings provide protection in areas where components may rub against each other, since the rubbingxe2x80x94especially high frequency rubbingxe2x80x94can erode the part. Various coatings may be used for this purpose, e.g., chromium carbide or cobalt-molybdenum-chromium-silicon coatings. The coatings are usually applied by thermal spray techniques, such as air plasma spray (APS), high velocity oxy-fuel (HVOF), and vacuum plasma spray (VPS).
The thermal spray techniques are quite suitable for applying wear coatings to many substrates. However, they are sometimes not effective for applying the coatings to regions of a substrate which are somewhat inaccessible, since the spray equipment may be too large and cumbersome for such regions. For example, it can be very difficult to thermally spray a wear coating on a flange or other surface of a turbine engine part. Moreover, the spray process, which may include one or more masking steps, is sometimes very time-consuming. Thus, new methods for efficiently applying wear coatings to inaccessible regions of a substrate would be welcome in the art.
One embodiment of this invention is a method for applying a wear coating on a surface of a substrate, comprising the following steps:
(a) attaching a foil which comprises the wear coating material to the substrate surface, and then
(b) fusing the foil to the substrate surface, so that the wear coating material adheres to the substrate.
The foil is often prepared by thermally spraying the wear coating material onto a removable support sheet. Exemplary thermal spray techniques are high velocity oxy-fuel and air plasma spray. The foil is then separated from the support sheet, prior to being fused to the substrate. The fusing step is usually carried out by brazing. The substrate is very often a superalloy material. This substrate can be a component of a turbine engine.
Examples of wear coating materials are chromium carbide and cobalt-molybdenum-chromium-silicon coatings. The disclosed methods greatly enhance the application of wear coatings to areas which are often inaccessible or difficult to coat by conventional deposition techniques.
A method for repairing a worn or damaged wear coating applied over a substrate is also described. The method comprises the following steps:
(i) removing the worn or damaged wear coating from a selected area on the substrate;
(ii) attaching a foil which comprises the wear coating material to the substrate surface, covering the selected area; and then
(iii) fusing the foil to the substrate, so that the wear coating material adheres to the selected area on the substrate.
Related articles are also described. They include a substrate, such as a turbine engine component, and a foil of the wear coating material disposed over the substrate. In preferred embodiments, the foil is fused to the substrate by a braze layer, to provide the wear coating in the desired location.
Further details regarding the various features of this invention are found in the remainder of the specification.